Vapour generators



Sept. 10, 1968 R. BAGLEY ETAL 3,400,689

VAPOUR GENERATORS Filed Aug. 25, 1966 6 Sheets-Sheet 1 Sept; 10, 1968 R. BAGLEY ETAL VAPOUR GENERATORS 6 Sheets-Sheet 2 Filed Aug. 25, 1966 Sept. 10, 1968 R. BAGLEY ETAL VAPOUR GENERATORS 6 Sheets-Sheet 3 Filed Aug. 25, 1966 Sept. 10, 1968 R. BAGLEY ETAL.

VAPOUR GENERATORS 6 Sheets-Sheet 4 Filed Aug. 25, 1966 Sept. 10, 1968 R. BAGLEY ETAL VAPOUR GENERATORS 6 Sheets-Sheet 5 Filed Aug. 25, 1966 p 10, 1963' R. BAGLEY ETAL. 3,400,689

' VAPOUR GENERATORS Filed Aug. 25, 1966 6 Sheets-Sheet 6 FIGS Unitcd States Patent ABSTRACT OF THE DISCLOSURE A forced flow vapour generator having upwardly inclined tubes in the lower portion and uprighttubes in the upper portion with the tubes supported by straps from above. The real wall of the furnace is provided with inclined tubes terminating adjacent the level of the lower boundary of a gas outlet with the upright tube extensions arranged in groups arranged axially of gas flow through the gas outlet and supported from above.

This invention relates to once-through, forced flow boilers and is especially concerned with boilers of this sort in which a gas pass is lined by a membrane wall, i.e., a wall in which tubes are connected together'side-by-side to provide a gas tight membrane.

One of the problems arising in the design of such walls is to ensure that the tubes are adequately cooled, even at low loads and several proposals have been made for dealing with this problem.

In one proposal, a wall is formed by vertical tubes connected in parallel to form a single pass. In order to ensure that even at low loads the mass flow is sufficient to cool the tubes adequately, the internal diameter of the tubes must be small. Not only is it expensive to manufacture such tubes to sufiiciently close tolerances but even a thin internal deposit would significantly increase the pressure drops occurring in them.

In an attempt to enable tubes of large diameter to be used it has been proposed that, to ensure adequate cooling of the tubes, at lower loads, say below 70% MCR, some of the fluid that has passed through the tubes should be recirculated through them. However, the lower mass 'flow at MCR leads to higher metal temperatures in the furnace; the tubes therefore operate at temperatures close to oxidation limits so that better quality tubes are necessary.

In a further attempt to enable tubes of larger diameter to be used, it has been proposed that they should form three passes, the tubes of one pass alternating with the tubes of the second pass and the tubes of both passes lying below the tubes of the third pass. In this arrangement, however, provision, which is expensive, must be made for mixing and this provision requires that the furnace should be operated at supercritical pressure with the consequent need for the feed pumps to operate against closed valves and for a flash tube to which the fluid flow can be diverted during start-up through reducing valves.

A disadvantage common to all these arrangements lies in the fact that the tubes are not all uniformly heated since the tubes at the corners of a gas-pass of rectangular cross-section will tend to be less highly heated than tubes extending along the middles of the sides of the gas pass.

According to the present invention, there is provided a once-through, forced-flow vapour generator having a length of upright gas pass bounded by a membrane lining formed from tubes connected for parallel [flow and having the spaces between the tubes closed, wherein each tube extends generally laterally of the length of gas pass and rises generally continuously.

In such a generator, the length of the tubes is not dic-' tated by the upright gas pass in whichthey are contained.

3,400,689 Patented Sept. 10, 1968 Some degree of freedom in the choice of tube size is thus possible, by variation of tube angle and membrane width, so that the tube size can be chosen to reconcile heat pickup requirements with economic factors. Moreover, the flud rises continuously in its passage through the lining tu es.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings in which FIGURE 1 shows somewhat diagrammatically a vertical section through a once-through, forced-flow vapour generator and superheater;

FIGURES 2a and 2b form a diagram showing the walls of the upright furnace chamber of this generator developed into a single plane;

FIGURE 3 is a detail on an enlarged scale seen from the rear, of a typical tube arrangement of the upper end of the rear wall of the furnace chamber.

FIGURE 4 is a perspective diagram illustrating certain details of the front and one of the side walls of the vapour generator;

FIGURE 5 is a perspective diagram illustrating certain details of the rear wall, lateral gas pass and one of the side walls of a modified form of the vapour generator; and

FIGURE 6 illustrates a tube connection included in the modification shown in FIGURE 5.

The once-through, forced-flow vapour generator and superheating unit illustrated in FIGURES 1 and 2 includes a furnace chamber 1 forming the lower end ofan upright gas pass 2 and fired by thirty circular burners, such as 3, in each of the front and rear walls, 4 and 5, of the gas pass 2. The lower end of the gas pass 2 ends in a hopper bottom 6, the front and rear walls 4a and 5a of which are convergent whilst the side walls are parallel.

A lateral gas pass 7 containing reheater tubes 7a extends from the upper end of the rear wall 5 and discharges combustion gases into the downpass 9 containing economiser tubes 9a. The walls of the gas pass 2 are lined, in a manner that will be described in more detail later, up to the level of the inlet to the lateral gas pass 7 by finned tubes that extend generally laterally but rise generally continuously. At the level of the inlet to the lateral gas pass 7 each of these tubes is connected to a vertical tube, the vertical tubes in the front and side walls being arranged side-by-side in groups 10. Each group 10 of tubes discharges into a header 14 (see FIGURE 4) and each header 14 is connected by means of a conduit 14a to a collector 15 extending centrally across the top of the gas pass. Conduits 14a extending towards each other from opposite sides of the gas pass are tied together, as is more clearly described in our co-pending application S.N. 575,157, and in this way they serve to withstand the pressures within the gas pass. The spaces between the groups 10 are filled by further groups 11 (see FIGURES 2 and 4) of vertical tubes, the tubes of the group 11 being supplied with fluid from the collector 15.

The front and side walls are suspended by means including vertical tension members 12 lying outside the boundary walls of the gas pass 2, being connected at their lower ends to the walls and supported by springs 13 at their upper ends. Each support strap or tension member 12 associated with the front and side walls lies alongside one of the groups 10 of vertical tubes. Similar tension members are associated with the rear wall in a manner that will be described in more detail later.

The support straps extend alongside the tube lining. internally of lagging, and are supported by a system of buckstays outside the lagging. The system includes horizontal buckstays 17 connected to the transversely extending tubes of the tube lining so that the tubes themselves withstand the forces urging opposed buckstays apart.

Platens of U-shaped superheater tubes 18 are suspended in the upper end of the pass, depending from beams 16 connected to certain of the springs 13.

Inlet headers are arranged around the lower end of the hopper 6, a space being left at the lower end through which gases may be recirculated. Tubes rise from the headers 20 to line the hopper 6 and each of these tubes leads to a tube 21 extending from the level A to the level B. The tubes 21 are controlled-bore tubes of 1 /2" outer diameter on a 2 inch pitch, the spaces between the tubes being closed by fins welded together along their edges. Between the levels A and B, each tube 21 encircles the gas pass more than once and rises continuously, at an angle of 15 to the horizontal, except where the routes of the tubes must be modified to accommodate the burners 3.

At the level B, each of the inclined tubes 21 leads to a generally vertically extending tube. These vertically extending tubes discharge into a common collector and then flows in a second pass through the further tubes, disposed in groups 11 between the vertical tubes in the front and side walls, as will be described with reference to FIGURE 4. A typical arrangement of the vertically extending tubes in the rear wall will now be described in more detail with especial reference to FIGURE 3.

At the level B, each of the tubes 21 that terminates in the rear wall is connected to an upright tube (see FIG- URE 3), the lower ends of which are uniformly spaced. The tubes 30 are then shaped and arranged to accommodate means for supporting the inclined tubes below them.

In the particular form shown in FIGURE 3, thirty-nine adjacent tubes 21 form a group, each set of three adjacent tubes 30 being shaped in a similar way. Thus tubes 30a rise to the levels Y, with a C-shaped deflection away from the furnace between level X and levels Y to skirt the beam 32. The tubes 30a then extend horizontally along the levels Y to the central position A where they extend in a plane parallel to the direction of flow of combustion gases through the gas pass 7 to a collector 33 connected at the top of the furnace setting to the collector 15.

The next set of three tubes, 30b, rise to the levels Z, being also provided with a C-shaped deflection away from the furnace between level X and levels 2 to skirt the beam 32. They then extend horizontally along the levels X to the position B where they extend in a fashion similar to the tubes 30a at position A.

Similarly, tubes 30c extend to position C, and tubes 30d, 30c and 30g to positions D, E, F and G respectively. The horizontal portions of tubes 30a, 300, 30s and 30g lie side-by-side at the levels Y and the horizontal portions of tubes 30b, 30d, 30] lie side-by-side at the levels Z.

The tubes 30 that lie to the right of the centre line extend in a generally similar manner to positions lying to the left of the centre line. Thus, tubes 30h, 30j and 301 extend to the positions H, J and C, having horizontal portions extending along the levels Y whilst tubes 30. 30b and 30m extend to the positions I, K and M having horizontal portions extending along the levels Z. T o skirt the beams 32, the tubes 3012-30m are provided between the levels X and Y and Z with C-shaped deflections extending towards the furnace chamber and the horizontal portions of tubes 30h-30m lie furnace-wards of the horizontal portions of tubes 3011-30 Each of the beams 32A, 32B, 32C and 32D, is in the form of a box beam and acts as a support for a strap 12. The lower ends of the straps 12 are connected to the lining of the lower part of the rear wall. As is indicated in FIGURE 3, certain of the tubes 30 are deflected to accommodate the straps 12. Beam 32A is supported from the portions of tubes 30 that extend along positions H and J. Beams 32B, 32C and 32D are similarly associated with the portions of tubes 30 that extend along positions K and M; A and C; and E and G, respectively. The tube portions at positions D are not used in supporting the wall. The tubes at positions I, L, B and F provide other support for the rear wall.

The tubes 30 at positions H and I are each provided with a stirrup 35 extending across the three tubes and resting on lugs 36 welded across the three tubes. Bars 37, attached to the stirrups 35 by a rocking mounting 38, extend down to the ends of the beam 32A and are attached thereto by connections 39 which penmit a limited pivotal movement between the 'bar 37 and the beam 32A.

The straps 12 depending from the beams 32A and 32C provide support for the rear wall in the region of the bottom of the burners and beams 32B and 32D provide support for the rear wall in the region just above this. Support is also provided at the upper end of the rear wall of the length of gas pass that is lined by inclined tubes. This support is associated with the tubes at positions I, L, B and F. At position I, for instances, the tubes 30 are provided with a further stirrup 40 resting on lugs indicated at 41, welded across the tubes. Bars 42 extend downwardly from rocking connections 43 to the stirrup 40, each being pivotally connected at 44 to a strap 42a welded at its lower end to a block 45 welded between adjacent tubes 21.

As is apparent from FIGURE 1, the tubes 30 are cranked at their upper ends to join the collectors 33 and the springs by which the tubes are suspended are connected to the tubes rather than the collector; the cranking of the tubes accommodates the relative movement of the tubes that will occur in operation. The springs by which the tubes at positions H, J, K, M, A, C, E and G. are supported are similar but the springs by which the tubes at positions I, L, B and F are supported are, whilst similar to each other, adapted to carry a smaller load than the spring by which the tubes at positions M, J, etc., are supported.

As is apparent from FIGURE 1, the groups of tubes at locations A to M extend upwardly through the nose arch and across the entrance to the lateral gas pass, the separation between the groups of tubes being sufiicient to permit the free flow of gases between them. Thus, forming the tubes 30 in a manner such described not only enables support to be provided for the rear wall without interfering with the free flow of combustion gases, but the horizontal components of the tubes enable relative expansions and contractions to be readily accommodated. It will be realised that the particular arrangement shown in FIGURE 3 may be modified to suit more, or less, than thirty-nine tubes. It will also be realised that since the beams 32 lie in what is, effectively, a tunnel their lengths need not be the same so that instead of one strap 12 being associated with each beam, any beam may carry two or more straps. Such longer beams are indicated in FIG- URE 2.

The tubes 51 forming the nose arch 50 extend in parallel from the horizontal headers 52, supplied by conduits 52a, and a seal is provided between these tubes and the tube 21 in the same manner shown in the detail in FIG- URE 3. Vertical blocks 53 are welded to the outer surfaces of the tubes 51 to provide a plane continuous surface whilst blocks 54 parallel to the tubes 21 are welded to the inner surface of the tubes 21 to provide a plane continuous surface in rubbing contact with that provided by the blocks 51. The other blocks, 56, that are connected to the tubes 21 provide a flush surface to which the easing for the wall may be connected. I

As is shown in FIGURE 4, the vertically upwardly extending tube lengths to which the inclined tubes 21 in the front and side walls are connected are arranged in groups 10. Each group 10 discharges into header 14 connected by means of a duct 14a to a collector 15 extending centrally across the gas pass. The collector 15 discharges into two downcomers 15a and the downcomers 15a supply a group of inlet headers 60. Each header lies outwardly of the corresponding wall of the gas pass and to it is connected a group 11 of vertically upwardly extending tube lengths, the outlet headers 61 of which lead eventually to the superheating platens. The spacers between the tube lengths in the groups 10 and 11 are closed by webs so that the lengths form a membrane wall.

The tube lengths in the groups 10 and 11 may be of the same diameter but, to take account of the greater vol ume of the fluid flowing through the tubes in the groups 11, the tube lengths in these groups may have a diameter larger than the tube lengths in the groups 10.

By the arrangement that has been illustrated in FIG- URE 4, mixing is achieved in a simple fashion and a second pass is conveniently introduced. Moreover, the headers 60 by which the tubes of the second pass are supplied may be disposed outside the gas pass Where they are accessible and not exposed directly to the heat of the furnace chamber.

In the modification indicated in FIGURE 5, inclined tubes are used to line the entire upright gas pass and the lateral gas pass. At the level B, the tubes 21 that terminate in the rear wall are connected to tube lengths (not shown in FIGURE 5) that extend upwardly across the lateral gas pass 7 in the manner already described. Each of the tubes 21 that terminates in the front and side wall is connected by an extension 65 to a collector 66 extending alongside, and outwardly of, these walls. The collector 65 discharges into a distributor 67, parallel to the collector 66 which feeds tubes 210 via ducts 68.

As is illustrated in FIGURE 6 each tube 21 is connected at its outlet end to a connector 69 in the form of two thimbles arranged back to back so that there is no pasasge between them. One thimble has a recess 69A of the same diameter as the tube 21 and discharges into the extension 65 extending laterally from it. The other thimble 69B has a recess of a larger diameter, the same as that of the tube 210 and is fed by the duct 68 extending laterally of the thimble 69B. Immediately before its connection to the connector 69, each tube 21 is bent slightly, at 21B so that the inclination of the tube 210 is greater than that of the major part of the tube 21 to which it is connected. By virtue of this greater inclination, the spacing between tubes 210 is the same as that between the tubes 21 although the diameter of the former is greater than that of the latter. The use of connectors in the form shown at 69 enable a smooth surface to be presented to the interior of the gas pass.

In the embodiment that has been described, the tubes 21 are formed into a membrane by means of fins projecting from the tubes and welded together. It is, however, envisaged that spacers may be welded along their edges to adjacent tubes or that a tangent tube arrangement might be used.

We claim:

1. A once-through forced flow vapour generator comprising Walls defining an upright gas pass of rectangular cross-section, means forming a gas outlet in a rear wall of said upright gas pass, said walls including parallel tube lengths, means for passing fluid in parallel flow relationship through said tube lengths, means filling the intertube spaces of said tubes to form a substantially gas tight gas pass wall structure, said rear wall tubes being inclined laterally and upwardly to rise generally continuously upwardly of said gas pass to terminate at the lower boundary of the gas outlet from said gas pass, a lateral gas pass extending from the gas outlet means of said upright gas pass, and each of the inclined tubes terminating at the lower boundary of said rear wall gas outlet means is connected at its upper end to a vertically upwardly extending tube length which traverses said gas outlet, said upwardly extending tube lengths being arranged in groups, the tube lengths in each group being aligned in the direction of gas flow through said lateral gas pass.

2. A forced-flow vapour generator as claimed in claim 1, in which the groups of tube lengths are incorporated in means supporting the upright gas pass rear wall that extends below the lateral gas pass.

3. A forced-flow vapour generator as claimed in claim 2, in which each upwardly extending tube length is in an upper and a lower part, the parts are displaced axially from each other across the width of the wall, and means for supporting the wall including tension members carried from said upper parts.

4. A forced-flow vapour generator as claimed in claim 3, in which each tension member is carried by a beam suspended from some of said tube length upper parts and the beams lie between tube lengths connecting upper and lower parts of the upwardly extending tube lengths.

S. A forced-flow vapour generator as claimed in claim 1, in which immediately below the entrance to the lateral gas pass, the tubes of said length of gas pass are provided, in the region at which they are connected to upright tube lengths, with filler blocks to which a casing for the length of gas pass is welded.

6. A forced-flow vapour generator as claimed in claim 5, in which tubes of said length of gas pass are provided, in the region at which they are connected to upwardly extending tube lengths that traverse the lateral gas pass with filler blocks to provide a generally flush surface, parts of tube lengths included in an arch extend past Said filler blocks and are themselves provided with filler blocks forming a generally fiush surface, the flush surfaces bearing against each other.

7. A forced flow vapour generator as claimed in claim 1 wherein the inclination of said inclined tubes in the front and side walls of said gas pass ends substantially at the level of the lower boundary of said gas outlet means, each of said side and front wall tubes at said level being connected at its upper end to one of a first set of vertically extending tube lengths extending to the upper end of the gas pass, tube lengths of a second set of vertically upwardly extending tube lengths are disposed between tube lengths of the first set, and means arranged for said second set of tubes to be cooled by fluid that has flowed through the tube lengths of said first set of tubes.

8. A forced flow vapour generator as claimed in claim 7, in which the vertically upwardly extending tube lengths are connected together to form a membrane wall.

9. A forced-flow vapour generator as claimed in claim 8, in which collector means receive fluid discharged from said first set of tube lengths, and conduit means connect said collector means with said second set of tube lengths for discharge thereto.

10. A forced flow vapour generator as claimed in claim 9, in which the tube lengths of the first set lie contiguously in groups and the tube lengths of the second set lie contiguously in groups alternating with the groups containin g tube lengths of the first set.

11. A forced flow vapour generator as claimed in claim 10, in which each of the groups in which tube lengths of the second set lie is provided with an inlet header lying externally of the wall.

12. A forced-flow vapour generator as claimed in claim 11, in which the tube lengths of the second set have the same diameter, the tube lengths of the first set have the same diameter and the latter is less than the former.

References Cited UNITED STATES PATENTS 3,298,360 1/1967 Michel 122-510 1,903,807 4/1933 Doble 122-250 FOREIGN PATENTS 1,334,730 7/1963 France.

909,537 10/1962 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner. 

